Just reproduced breakage caused by iOS 14. I missed this because I only tested iOS 14 on my newer iPad Pro. The bug makes the sculptures look blocky, and it will erase the surface data if autosave kicks in.
I’m not sure the exact cause, but I have work around that I’ll submit shortly.
WARNING: this breakage will destroy your sculptures if you open them. I’m sorry about that!
Fix coming ASAP.